Scanning transmission electron microscope and electron energy loss spectroscopy

Abstract

The present invention provides a scanning transmission electron microscope which is capable of setting an acceptance angular range of an energy loss spectrometer independent of an acceptance angular range of a scattered electron detector, and makes it unnecessary to change a condition for the energy loss spectrometer with respect to a change in the acceptance angular range of the scattered electron detector. In such a scanning transmission electron microscope equipped with the energy loss spectrometer, a first rotationally symmetric type magnetic lens for setting an acceptance angle of an electron scattered by a specimen is disposed above the scattered electron detector for detecting the electron, a second rotationally symmetric type magnetic lens is disposed between the scattered electron detector and the energy loss spectrometer, the first rotationally symmetric type magnetic lens sets the acceptance angle of the scattered electron, and the second rotationally symmetric type magnetic lens sets an object point of the energy loss spectrometer.

1. A scanning transmission electron microscope comprising:
 an energy loss spectrometer; 
 a first rotationally symmetric type magnetic lens for setting an acceptance angle of an electron scattered by a specimen, said first rotationally symmetric type magnetic lens being disposed above a scattered electron detector for detecting the electron; and 
 a second rotationally symmetric type magnetic lens disposed between the scattered electron detector and the energy loss spectrometer, 
 wherein the first rotationally symmetric type magnetic lens sets the acceptance angle of the scattered electron, and 
 wherein the second rotationally symmetric type magnetic lens sets an object point of the energy loss spectrometer. 
 
   
   
     2. A scanning transmission electron microscope utilized in combination with an energy loss spectrometer, comprising:
 a specimen table for holding a specimen; 
 an illumination optical system for scanning a converged electron on the specimen; 
 a scattered electron detector for detecting an electron scattered by the specimen; 
 an objective lens disposed between the specimen table and the scattered electron detector; 
 a diaphragm having an aperture for capturing an electron transmitted through the specimen and having passed through the scattered electron detector into the energy loss spectrometer; 
 a first rotationally symmetric type magnetic lens of at least one stage disposed in a stage above the scattered electron detector; and 
 a second rotationally symmetric type magnetic lens of at least one stage disposed in a stage below the scattered electron detector, 
 wherein angular ranges for all or some of electrons transmitted through the scattered electron detector are selectively captured into the energy loss spectrometer independent of an angular range for the electron captured into the scattered electron detector. 
 
   
   
     3. The scanning transmission electron microscope according to  claim 2 , wherein the objective lens and the diaphragm are disposed in such a manner that an angle α of incidence of the converged electron into the objective lens and an acceptance angle β of an electron incident into the diaphragm satisfy β≧α/M (where M indicates a magnification based on an integrated lens action of the objective lens, the first rotationally symmetric type magnetic lens and the second rotationally symmetric type magnetic lens). 
   
   
     4. A scanning transmission electron microscope utilized in combination with an energy loss spectrometer, comprising:
 a specimen table for holding a specimen; 
 an illumination optical system for scanning a converged electron on the specimen; 
 a scattered electron detector for detecting a scanning electron scattered by the specimen; 
 an objective lens disposed between the specimen table and the scattered electron detector; 
 a diaphragm provided with an aperture for capturing a scanning electron transmitted through the specimen into the energy loss spectrometer; 
 a first projector lens disposed between the objective lens and the scattered electron detector; and 
 a second projector lens disposed between the scattered electron detector and the diaphragm, 
 wherein a first image obtained through the objective lens, of the electron transmitted through the specimen is projected onto a second image by the first projector lens, and the second image is projected onto a third image by the second projector lens. 
 
   
   
     5. The scanning transmission electron microscope according to  claim 4 , wherein the first image obtained through the objective lens, of the electron transmitted through the specimen is projected onto a second image by the first projector lens, the second image is projected onto a third image by the second projector lens, and the third image coincides with an object point of the energy loss spectrometer. 
   
   
     6. The scanning transmission electron microscope according to  claim 4  or  5 , further comprising a transmitted electron detector for detecting the electron transmitted through the specimen. 
   
   
     7. The scanning transmission electron microscope according to  claim 6 , wherein the scattered electron detector has an annular shape provided with an opening through which an optical axis of the electron transmitted through the specimen passes, and the transmitted electron detector is placed on the optical axis and disposed between the scattered electron detector and the diaphragm. 
   
   
     8. The scanning transmission electron microscope according to  claim 4  or  5 , further comprising first control means for reading a signal detected by the scattered electron detector in synchronization with a scanning cycle of the electron scanned on the specimen. 
   
   
     9. The scanning transmission electron microscope according to  claim 4  or  5 , wherein each of the first projector lens and the second projector lens is a rotationally symmetric type magnetic lens. 
   
   
     10. The scanning transmission electron microscope according to  claim 8 , further comprising:
 display means for displaying the signal detected by the scattered electron detector as an image; and 
 second control means for reading a signal detected by the transmitted electron detector in synchronization with a scanning cycle of the electron scanned on the specimen, 
 wherein both a dark field image formed from the signal detected by the scattered electron detector and a bright field image formed from the signal detected by the transmitted electron detector are displayed on the display means. 
 
   
   
     11. The scanning transmission electron microscope according to  claim 10 , further comprising:
 detector drive means for moving the transmitted electron detector, 
 wherein the transmitted electron detector is withdrawn from on the optical axis upon execution of spectroscopy. 
 
   
   
     12. The scanning transmission electron microscope according to  claim 11 , further comprising:
 mode switching input means for selecting a dark field image observation mode, a bright field image observation mode or a mode for simultaneously observing a dark field image and a bright field image; and 
 third control means for controlling the detector drive means, 
 wherein the third control means operates the detector drive means in accordance with an input to the mode switching input means and withdraws the transmitted electron detector from on the optical axis or moves the same onto the optical axis. 
 
   
   
     13. An electron energy loss spectroscopy using a scanning transmission electron microscope, comprising the steps of:
 scanning an electron generated from an electron source on a specimen through an illumination optical system; 
 detecting the intensity of each electron scattered by the specimen by a scattered electron detector to acquire a dark field image; 
 detecting the intensity of each of the electrons having passed through the scattered electron detector by a transmitted electron detector to acquire a bright field image; 
 launching each electron having passed through the scattered electron detector into an energy loss spectrometer to acquire an energy loss spectrum; 
 selectively capturing angular ranges for all or some of the electrons having passed through the scattered electron detector into the energy loss spectrometer by a first projector lens disposed in a stage above the scattered electron detector and a second projector lens disposed in a stage below the scattered electron detector, independent of an angular range of each electron captured into the scattered electron detector, thereby performing energy loss spectroscopy. 
 
   
   
     14. The electron energy loss spectroscopy according to  claim 13 , further comprising the steps of forming a first image of the electron on the specimen by a post-magnetic field objective lens, projecting the first image on a second image by the first projector lens and projecting the second image on a third image by the second projector lens. 
   
   
     15. The electron energy loss spectroscopy according to  claim 13 , further comprising the steps of forming a first image of the electron on the specimen by a post-magnetic field objective lens, projecting the first image on a second image by the first projector lens, projecting the second image on a third image by the second projector lens, and allowing the third image to coincide with an object point of the energy loss spectrometer. 
   
   
     16. The electron energy loss spectroscopy according to  claim 13 , further comprising the step of changing an acceptance angle of the transmitted electron detector by the second projector lens independent of an acceptance angular range of the scattered electron detector.